Valve for controlling fluids

ABSTRACT

A valve for controlling fluids is proposed that for its actuation cooperates with a piezoelectric actuator ( 2 ). To compensate for changes in the length of the piezoelectric actuator ( 2 ) in the stroke direction that are caused by temperature changes, a compensation element ( 7 ) is provided, which comprises a material that has a coefficient of thermal expansion that is approximately equivalent to that of the piezoelectric actuator ( 2 ). The piezoelectric actuator ( 2 ) and compensation element ( 7 ), upon a certain temperature change, exhibit a comparable change in their length in the stroke direction. As a result, the change in length of the piezoelectric actuator with the temperature is compensated for. The valve is intended for use in fuel injection devices for internal combustion engines.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a 35 USC 371 application of PCT/DE 00/02534, filed on Aug. 1,2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a valve for controlling fluids and particularlyto an improved valve having an actuator piston actuated by apiezoelectric actuator.

2. Description of the Prior Art

One such valve is known from European Patent Disclosure EP 0 477 400 A1,for instance. There, the actuating piston of the valve member isdisposed displaceably in a smaller-diameter part of a stepped bore,while conversely a larger-diameter piston, which is moved by apiezoelectric actuator, is disposed in the larger-diameter part of thestepped bore. Enclosed between the two pistons is a hydraulic chamber,such that when the larger piston is moved by the piezoelectric actuator,the actuating piston of the valve member is moved by a distance that isincreased by the boosting ratio of the stepped bore diameters. The valvemember, the actuating piston, the larger-diameter piston, and thepiezoelectric actuator are located successively on the same axis.

If a piezoelectric actuator is to be usable as a control element, thechange in length as a function of temperature must be compensated for.Since the stroke attainable by means of a piezoelectric actuator amountsto only between about 1/1000 and 1.5/1000 of its length, for manyapplications it is necessary for this tiny stroke to be boosted. Thedifferent coefficients of thermal expansion of the various materialsused cause settling effects, which are sometimes greater in the strokedirection than the possible stroke caused by the piezoelectric actuatorelement.

To create a compensation for such variations, in the valve disclosed inEP 0 477 400 A1, a defined leak is provided in the hydraulic chamber.Upon slow changes in the valve structure, of the kind that can be causedtemperature changes, for instance, the hydraulic fluid can escapethrough the leak and thus compensate for the effects in the strokedirection. The viscosity of the hydraulic fluid is selected such thatupon rapid changes, of the kind caused by the piezoelectric actuator,the hydraulic fluid does not escape through the leak, and the deflectionof the piezoelectric actuator is transmitted to the actuating piston.This compensation is very complicated and expensive, because it requiresvery close tolerances in the production of the pistons in order to beable to create a defined leak in the form of an annular gap between thepiston and the surrounding cylinder wall. Furthermore, divertedhydraulic fluid must be returned to the hydraulic chamber again, forwhich purpose suitable devices must also be provided.

SUMMARY OF THE INVENTION

The valve for controlling fluids according to the invention has theadvantage over the prior art that it is very simple in structure and canbe produced economically. A ratio of coefficients of thermal expansionof approximately or equal to 1 is understood to mean values between 1.0and approximately 1.1. In the ideal case, the ratio is 1.

In the valve of the invention, this means a markedly reduced number ofparts. As a result, putting together the valve is simplified, andcalibration operations are fewer, since fewer parts have to becalibrated. This means in particular that the production and assemblycosts for the valve can be reduced markedly.

In a preferred exemplary embodiment of the invention, the compensationelement is embodied as a cylindrical ring element, which surrounds thepiezoelectric actuator. By means of this design of the compensationelement, an optimal compensatory effect can be assured, since thepiezoelectric actuator and the compensation element are exposed to thesame temperature effects. This design of the compensation element alsodictates a simple design of the valve of the invention.

Alternatively, it is also possible in an advantageous embodiment todispose the compensation element merely parallel to the piezoelectricactuator. As a result, on the one hand the compensation element canassume various shapes, for instance cylindrical, or triangular or squarein cross section, and so forth. In this respect, in terms of its shapethe compensation element can be adapted to the spatial conditions of thevalve design. By this means it can also be assured that thepiezoelectric actuator and the compensation element are always locatedquite close together, so that the temperature factors affect bothelements to the same extent.

In a further feature, the piezoelectric actuator and compensationelement are disposed spatially near one another, preferably in a commonchamber. In that case, temperature changes act in the same way on bothparts, so that the changes in length of the piezoelectric actuator andthe compensation element compensate for one another.

If the coefficients of thermal expansion of the piezoelectric actuatorand compensation element are the same, then advantageously a design isselected in which the effective length of the compensation element isequivalent to the length of the piezoelectric actuator. The term“effective length” is understood to mean the expansion of thecompensation element parallel to the axis of the piezoelectric actuatorthat is available for an expansion of the compensation element in thedirection of the axis of the piezoelectric element.

It has proved to be suitable for the operation of the valve if thecompensation element comprises Invar®.

In an advantageous embodiment, an air gap is provided between thetransmission element and the booster. The air gap amounts to only a fewmicrometers. If the piezoelectric actuator and the compensation elementdo not have precisely the same coefficient of thermal expansion, then inthis way a compensation for residual error can be achieved.

Advantageously, the transmission element includes a tie rod, and thecompensation element is part of the tie rod. In this way, thetransmission element is very simple to produce, and only slight problemsfrom production variations occur.

A sturdy embodiment of the valve is attained if the booster is embodiedas a mechanical booster, preferably as a lever.

In an advantageous feature of the invention, a support point of thelever is located in the axis of the piezoelectric actuator.

If the coefficients of expansion of the piezoelectric actuator andcompensation element are not precisely the same, or if a longitudinalexpansion of other materials is to be compensated for along with thelongitudinal expansion of the piezoelectric actuator, then it isadvantageous if the effective length of the compensation element is notequal to the length of the piezoelectric actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are explained in further detailherein below, in conjunction with the drawings, in which:

FIG. 1 is a sectional view of a fuel injection valve in a firstexemplary embodiment

FIG. 2 is a version of the valve member as a double-acting valve;

FIG. 3 a fuel injection valve in a second exemplary embodiment, insection;

FIG. 4 a fuel injection valve in a third exemplary embodiment, insection; and

FIG. 5 is fuel injection valve in a fourth exemplary embodiment, insection.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a valve for controlling fluids in a first exemplaryembodiment of the invention. The valve includes a housing 1, in which apiezoelectric actuator 2 is disposed. The free end of the piezoelectricactuator 2 is adjoined by a transmission element 3, which includes a tierod 5 extending parallel to the axis 4 of the piezoelectric actuator 2.The piezoelectric actuator is prestressed by a cup spring 6. Acompensation element 7, preferably made from Invar®, is integrated withthe tie rod 8. The compensation element 7 is connected to the tie rod 5here by means of a threaded connection. Other types of connection, suchas adhesive bonding, can also be employed, however. The compensationelement 7 and piezoelectric actuator 2 are approximately equal in lengthand are disposed spatially close together in a common chamber. The tierod 5 is extended in the form of a leg 8, which forms the support pointwith the support point axis 9 for the lever 10. In FIG. 1, the supportpoint axis 9 is not aligned with the axis 4 of the piezoelectricactuator. However, in a preferred embodiment of the valve of theinvention for controlling fluids, the support point axis 9 can also bealigned with the axis 4 of the piezoelectric actuator 2.

Between the leg 8 and the lever 10, an air gap 11 is formed, in theposition of repose. The air gap 11 amounts to only a few micrometers.The lever 10 is supported on the bearing 12, which divides the lever 10into a shorter lever arm of length B and a longer lever arm of length A.The ratio A/B determines the boosting ratio. The lever 10 is prestressedby the compression spring 14, acting on the longer lever arm in theopening direction of the valve member 13. The longer lever arm of lengthA acts on the piston 15 of the valve member 13. In the position ofrepose, the piston 15 is pressed against the valve seat 17 by thecompression spring 16, which has a higher spring constant than thecompression spring 14.

In FIG. 1, the valve of the invention is shown as a single-actingoutlet/inlet valve. However, an embodiment as a double-acting valve isalso possible. Such an embodiment is shown in FIG. 2. This valve differsfrom the valve shown in FIG. 1 only in terms of the valve member. InFIG. 2, therefore only this portion is shown. The piston 15 can thencome into contact with both an upper seat 18 and a lower seat 19. Theinflow to the valve takes place via an inflow line 20, which in thevalve shown extends from below up to the valve housing, while theoutflow line 21 is disposed opposite the inflow line 20, above the uppervalve seat.

Mode of Operation

In operation of the valve using a piezoelectric actuator 2, it isnecessary to compensate for changes in length of the piezoelectricactuator 2, the valve itself, or the valve housing 1. The compensationelement 7 serves this purpose and also provides residual errorcorrection for the air gap 11.

Each time the piezoelectric actuator 2 is turned on, the transmissionelement 3 is lifted, counter to the prestressing of the cup spring 6.The stroke is transmitted via the tie rod 5 and the leg 8 to the shorterlever arm of the lever 10. Determined by the ratio of lever arm lengthsA/B, the stroke of the piezoelectric actuator 2 is boosted to acorresponding stroke of the longer lever arm (A). The lever arm (A)moves in the opening direction of the valve member 13 and moves thepiston 15 downward, counter to the force of the spring 16, as a resultof which the line 21 is opened. When the piezoelectric actuator 2 isturned off, the transmission element 3 drops back into its position ofrepose, and the piston 15 is pressed against the seat 17 again by theforce of the spring 16, as a result of which the line 21 is closedagain. By the force of the spring 14, the lever 10 is returned to itsposition of repose, and the air gap 11 forms again.

In the version as a double-acting valve, shown in FIG. 2, accordinglywhen the piezoelectric actuator 2 is turned on, the piston 15 is pressedagainst the lower valve seat 19, and the inflow line 20 is closed andthe outflow line 21 is opened. In the OFF state, correspondingly, theinflow 20 is opened and the outflow 21 is closed.

Upon temperature changes, the length of the piezoelectric actuator 2changes along its axis in the stroke direction. To compensate for thischange in length, the compensation element 7 is provided. It is made forinstance from Invar® and has a coefficient of thermal expansion similarto that of the piezoelectric actuator 2. For the same temperaturechange, it therefore exhibits comparable changes in length. Since thepiezoelectric actuator 2 and compensation element 7 are disposedspatially close together in the same chamber, they are subject to thesame temperature factors. Thus both parts exhibit virtually the samechanges in length. Slight differences in the coefficients of thermalexpansion, which cause a residual error, are intercepted by the air gap11. The air gap can be increased or decreased in size within certainlimits, without affecting the function of the valve. The dimensioning ofthe air gap 11 is selected such that in both the cold state and athigher temperatures, no warping or excessive tolerances in thetransmission of the stroke of the piezoelectric actuator 2 to the piston15 will occur. If with increasing temperature the piezoelectric actuator2 expands more markedly than the compensation element 7, then in thisstate at room temperature a somewhat larger air gap 11 must be provided,which becomes smaller as the temperature rises. Conversely, if withincreasing temperature the compensation element 7 expands more markedlythan the piezoelectric actuator 2, then in this state at roomtemperature a very small air gap 11 must be provided, which becomeslarger with increasing temperature.

FIG. 3 shows a valve for controlling fluids in a second exemplaryembodiment of the invention. Although this valve 30 in terms of itsconstruction differs considerably from the valve 1 of the firstexemplary embodiment, the compensation element 31 used in the valve 30is based on the same mode of operation as the compensation element 7 ofthe first exemplary embodiment.

The valve 30 includes a housing 32, in which a piezoelectric actuator 33is disposed. Here the piezoelectric actuator 33 is prestressed insidethe housing 32 by means of a prestressing element 34 in the form of asealing spring and a piston 35. At the same time, the compensationelement 31, which extends substantially concentrically and annularlyaround the piezoelectric actuator 33, is prestressed against the housing32 of the valve 30 by the sealing spring 34.

The end of the piezoelectric actuator 33 opposite the piston 35 isadjoined by the piston 36, which is tapered on its free end and afterits tapered point ends in a ball 37. The ball 37, as shown in FIG. 3,has a circumferential ring 38, by means of which the ball 37 isprestressed by a spring 39 into a first seat 40.

When electric current is delivered to the piezoelectric actuator 33, thepiston 36 along with the ball 37 is shifted downward in terms of FIG. 3,putting the ball 37 into close contact with the second seat 41.

In the usual way, the second seat 41 is followed by the outflow throttle42, the control chamber 43 with the inflow throttle 44, and on to theinjection nozzle, not shown. Since the components leading onward arewell known, they will not be described or shown here.

Also in the second exemplary embodiment of the valve of the invention,the same principle of the piezoelectric actuator 33 and compensationelement 31 as in the first exemplary embodiment is employed. That is,upon temperature changes, the length of the piezoelectric actuator 33changes along its axis in the stroke direction. To compensate for thischange in length, the compensation element 31 is provided. It isproduced from Invar® or ceramic, for instance, and has a coefficient ofthermal expansion that is similar or preferably identical to that of thepiezoelectric actuator 33. For the same temperature change, it thereforeexhibits comparable changes in length. Since the piezoelectric actuator33 and compensation element 31 are disposed spatially near one anotherin the same chamber, they are subject to the same temperature factors.Thus both parts exhibit virtually the same changes in length.

However, if slight differences in the coefficient of thermal expansionoccur, resulting in a residual error, then this residual error can beintercepted by means of a gap 45 embodied between the piston 36 and theball 37. The air gap can be increased or decreased in size withincertain limits, without affecting the function of the valve. Thedimensioning of the air gap 45 is selected such that in both the coldstate and at higher temperatures, no warping or excessive tolerances inthe transmission of the stroke of the piezoelectric actuator 33 to thepiston 36 will occur. If with increasing temperature the piezoelectricactuator 33 expands more markedly than the compensation element 31, thenat room temperature a somewhat larger air gap 45 must be provided, whichbecomes smaller as the temperature rises. Conversely, if with increasingtemperature the compensation element 31 expands more markedly than thepiezoelectric actuator 33, then at room temperature a very small air gap45 must be provided, which becomes larger with increasing temperature.

FIG. 4 shows a third exemplary embodiment of a valve 50 of theinvention. Since the valve 30 of the second exemplary embodiment largelymatches the valve 50 of the third exemplary embodiment in terms of itsdesign, only the differences between the two valves will be addressedbelow.

The valve 50 again includes a housing in which a piezoelectric actuator53 is disposed. However, here the stroke of the piezoelectric actuator53 is not transmitted directly to the piston 56; instead, as in thefirst exemplary embodiment of FIG. 1, a transmission element 52 isconnected to the piezoelectric actuator 53. Furthermore, thetransmission element 52 is connected to a compensation element 51, andthe compensation element 51 is disposed parallel to the piezoelectricactuator 53. Finally, the compensation element 51 engages a lever 54,which in turn is connected to the piston 56. Thus in the valve 50 of thethird exemplary embodiment, the same conditions are obtained as for thecorresponding components of the first exemplary embodiment of FIG. 1,especially in terms of the mode of operation of the piezoelectricactuator 53 and the compensation element 51. In this respect it shouldbe pointed out that the compensation elements of the first and thirdexemplary embodiments can have various symmetrical shapes in crosssection, as needed. Attractive examples are a round, triangular orsquare cross-sectional shape.

Finally, in FIG. 5 a fourth exemplary embodiment of a valve 60 of theinvention is shown. This valve 60 of FIG. 5 differs from the valve 50 ofFIG. 4 in that the compensation element 61 is prestressed by aprestressing element in the form of a sealing spring 62. To that end,the compensation element 61 is connected on its upper end, in terms ofFIG. 5, to a piston 63, which in turn is connected to a transmissionelement 64 and which is engaged by the sealing spring 62.

Also in the valve 60 of FIG. 5, unlike the valve 50 of FIG. 4, a guide65 is provided, which extends in the axis of the compensation element 61along with a piston 66 as far as the control valve with the first seat67 and the second seat 68.

As a result, the compensation element 61 of the valve 60 in conjunctionwith the piezoelectric actuator 69 again dictates the same mode ofoperation as in the first-mentioned exemplary embodiments 1-3. Inaddition, it is naturally also possible in the third and fourthexemplary embodiments of FIGS. 4 and 5 for an air gap to be embodiedbetween the piston and the associated valve member, in order tocompensate for the residual error, explained in conjunction with thefirst and second exemplary embodiments, in the event of differences inthe coefficients of thermal expansion between the piezoelectric actuatorand the compensation element.

It has also been found that an especially good function of the valve ofthe invention is attained if the piezoelectric actuator and the controlvalve are located in virtually the same axis, and the piezoelectricactuator and the compensation element are located quite close together.

In conclusion, it should be noted that the valve of the invention inaccordance with the various exemplary embodiments can be designed aseither single- or double-acting. The embodiments according to theinvention can also be employed in a 2/3-way control valve. It is also acommon feature of the exemplary embodiments of FIGS. 1-3 that theapplicable piezoelectric actuator is prestressed by a prestressingspring of low stiffness and with high prestressing force.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed is:
 1. A valve for controlling fluids, comprising apiezoelectric actuator (2), whose stroke is transmitted to a valvemember (13) by means of a transmission element (3), and a compensationelement (7) spaced apart from the piezoelectric actuator (2), thecompensating element compensating for temperature fluctuations of thepiezoelectric actuator (2), and the ratio of the coefficient of thermalexpansion of the piezoelectric actuator (2) and the coefficient ofthermal expansion of the compensation element (7) is approximately orequal to 1, the compensation element (7; 51) being embodied in rodlikeform and disposed parallel to and spaced apart from the piezoelectricactuator (2; 53).
 2. The valve for controlling fluids of claim 1 whereinthe piezoelectric actuator (2) and compensation element (7) are disposedspatially near one another, preferably in a common chamber.
 3. The valvefor controlling fluids of claim 2 wherein the effective length of thecompensation element (7) is equivalent to the length of thepiezoelectric actuator (2).
 4. The valve for controlling fluids of claim2 wherein the compensation element (7) comprises Invar® or ceramic. 5.The valve for controlling fluids of claim 2 further compromising an airgap (11) between the transmission element (3) and the booster (10). 6.The valve for controlling fluids of claim 2 wherein the transmissionelement (3) includes a tie rod (5), and wherein the compensation element(7) is part of the tie rod (5).
 7. The valve for controlling fluids ofclaim 2 wherein the transmission element (3) transmits the stroke to thebooster (10), and the booster is embodied as a mechanical booster,preferably as a lever.
 8. The valve for controlling fluids of claim 1wherein the effective length of the compensation element (7) isequivalent to the length of the piezoelectric actuator (2).
 9. The valvefor controlling fluids of claim 8 wherein the compensation element (7)comprises Invar® or ceramic.
 10. The valve for controlling fluids ofclaim 8 further comprising an air gap (11) between the transmissionelement (3) and the booster (10).
 11. The valve for controlling fluidsof claim 8 wherein the transmission element (3) includes a tie rod (5),and wherein the compensation element (7) is part of the tie rod (5). 12.The valve for controlling fluids of claim 1 wherein the compensationelement (7) comprises Invar® or ceramic.
 13. The valve for controllingfluids of claim 12 further comprising an air gap (11) between thetransmission element (3) and the booster (10).
 14. The valve forcontrolling fluids of claim 1 further comprising an air gap (11) betweenthe transmission element (3) and the booster (10).
 15. The valve forcontrolling fluids of claim 14 wherein the transmission element (3)includes a tie rod (5), and wherein the compensation element (7) is partof the tie rod (5).
 16. The valve for controlling fluids of claim 14wherein the transmission element (3) transmits the stroke to the booster(10), and the booster is embodied as a mechanical booster, preferably asa lever.
 17. The valve for controlling fluids of claim 14 wherein asupport point of the lever (10) is located in the axis (9) of thepiezoelectric actuator.
 18. The valve for controlling fluids of claim 1wherein the transmission element (3) includes a tie rod (5), and whereinthe compensation element (7) is part of the tie rod (5).
 19. The valvefor controlling fluids of claim 1 wherein the transmission element (3)transmits the stroke to the booster (10), and the booster is embodied asa mechanical booster, preferably as a lever.
 20. The valve forcontrolling fluids of claim 19 wherein a support point of the lever (10)is located in the axis (9) of the piezoelectric actuator.